Microwave band gap and cavity mode in spoof–insulator–spoof waveguide with multiscale structured surface

Abstract

We propose a multiscale spoof-insulator-spoof (SIS) waveguide by introducing periodic geometry modulation in the wavelength scale to a SIS waveguide made of perfect electric conductor. The MSIS consists of multiple SIS subcells. The dispersion relationship of the fundamental guided mode of the spoof surface plasmon polaritons (SSPPs) is studied analytically within the small gap approximation. It is shown that the multiscale SIS possesses microwave band gap (MBG) due to the Bragg scattering. The "gap maps" in the design parameter space are provided. We demonstrate that the geometry of the subcells can efficiently adjust the effective refraction index of the elementary SIS and therefore further control the width and the position of the MBG. The results are in good agreement with numerical calculations by the finite element method (FEM). For finite-sized MSIS of given geometry in the millimeter scale, FEM calculations show that the first-order symmetric SSPP mode has zero transmission in the MBG within frequency range from 4.29 GHz to 5.1 GHz. A cavity mode is observed inside the gap at 4.58 GHz, which comes from a designer "point defect" in the multiscale SIS waveguide. Furthermore, ultrathin MSIS waveguides are shown to have both symmetric and antisymmetric modes with their own MBGs, respectively. The deep-subwavelength confinement and the great degree to control the propagation of SSPPs in such structures promise potential applications in miniaturized microwave device.

Long-Range Spoof Surface Plasmons(LRSSP) on the Asymmetric Double Metal Gratings

“…In conclusion, the asymmetric double metal gratings are proposed to support LRSSP. Symmetric structure is simple [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], however, the asymmetry can provide a new degree of freedom to control SSP mode on this kind of double-corrugated plasmonic structure. Besides, the propagation losses of SRSSP can be reduced largely within asymmetric regime.…”

“…The other anti-symmetric lossy SSP mode is termed as short-range SSP (SRSSP). Double metal gratings have been proposed for a series of passive devices such as mode converter and modulators [17][18][19], sensors [20][21][22], waveguides, filters [23][24][25][26] and also some novel active devices such as THz laser or beam emitters [27][28][29]. For these demonstrated studies on double metal grating, the metal is mostly assumed as perfect electric conductor and the damping losses are ignored.…”

“…However, for practical applications, it is not always conveniently the same with each other between the upper and lower metal grating thus the asymmetry on the structure should be specifically considered and investigated. Additionally, the asymmetry can provide a new degree of freedom to tailor SSP mode on this kind of doubly-corrugated plasmonic platform [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”

“…More importantly, the evolutions of LRSSP and SRSSP dispersion modes along with various asymmetries on the structure are not conducted so far. To this end, the asymmetric double metal gratings are here proposed to support LRSSP modes, which can break the strictly symmetric limitation of conventional structure [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Besides, the modal characteristics of both LRSSP and SRSSP mode with various asymmetric degrees are studied and analyzed in THz band both theoretically and numerically.…”

Spoof surface plasmon polaritons of complementary periodic units with negative group velocity effect

“…For SPP modes with insulator‐metal‐insulator (IMI) three‐layer guided‐wave structures, the odd modes generated by the coupling of two interface modes can exhibit negative group velocity in a certain band 19 . The same is true for the odd modes of the three‐layer SSPP waveguides, the spoof‐insulator‐spoof (SIS) structures 20 . Therefore, we believe that the NGV effect can be improved by enhancing the asymmetry of odd modes.…”